II. MEASUREMENT. 1 ,53 



II. MEASUREMENT. 



705. Revolving Drum, for determining pitch of note. 



Prof. Frederick Guthrie, F.R.S. 



The styles attached to two vibrating forks mark sinuosities on the blackened 

 surface of the drum when it turns and advances on its screw axis. The 

 pitch of the notes is thus compared. 



705a. Apparatus, by M. Regnault, for ascertaining the velocity 

 of sound. College of France, Paris. 



706. Acoustic Apparatus, for ascertaining the velocity of 

 transmission of sound through water, used in 1826 on the Lake of 

 Geneva at a distance of 13,487 metres, and subsequently in 1841 

 at a distance of 35,000 metres. 



Professor Daniel Colladon, Geneva. 



Acoustic apparatus used in 1826 and 1841, during a series of experiments 

 upon the transmission of sound through water, and upon the direct measure- 

 ment of the velocity of sound in the water of the Lake of Geneva. 



Memoires de P Academic des Sciences de 1'Institut de France, savants 

 etrangers, sciences mathematiques et physiques, vol. 5, 267 and following 

 pages. Comptes-rendus de PInstitut, vol. 13, p. 439, seance 23rd August 

 1841. 



N.B. With this instrument it is possible in calm weather to hear, at the 

 distance of more than a hundred kilometres, the reverberation of blows 

 struck upon a bell of about half a ton weight immersed in the water, and 

 thus to use it as a submarine telegraph, or for transmitting signals in foggy 

 weather. 



707. Apparatus for marking Tuning-fork Vibrations. 



Professor L. von Babo, Freiburg, Breisgau. 



707a. Original Apparatus, by Duliamel, for registering 

 vibrations. Polytechnic School, Paris. 



708. Helmholtz' Double Siren. 



H. Lloyd, Trinity College, Dublin. 



709. Double Siren, such as was employed by Professor 

 Helmholtz in his researches on sound. 



Prof. Frederick Guthrie, F.R.S. 



710. Siren, of card-board, with four ciryles of holes, 64, 80, 

 96, and 128, giving major chord. Made by Yeates and Sons. 



Prof. W. F. Barrett. 



The above is provided with an air-chest and four keys, so that any or all 

 the circles of holes can be made to sound at pleasure. 



711. Siren, an instrument for showing the number of 

 vibrations corresponding to a given note. Elliott Brothers. 



